Method for using auxiliary filtering agents for filtration purposes

ABSTRACT

The invention relates to a method for filtering liquids, especially biological liquids. A filter ( 1 ) is deposited with the auxiliary filtering agent during a pre-deposition phase. In an ensuing filtration phase, the infiltrate is filtered by adding an auxiliary filtering agent. The auxiliary filtering agent forms a filter cake during the pre-deposition phase and the filtration phase. The auxiliary filtering agent is deposited during the pre-deposition phase, the proportion of regenerated auxiliary filtering agent being 30%, especially 0%. During the filtration phase, an auxiliary filtering agent is added, consisting predominantly, especially almost fully, of regenerated auxiliary filtering agent. The regenerated auxiliary filtering agent is treated with a medium over the whole pH value spectrum.

The invention concerns a method for filtering liquids of the typeindicated in the generic part of claim 1.

The use of diatomaceous earth, perlites and/or cellulose as filter aidsin the filtration of liquids is known. For the filtration of biologicalliquids, in particular beer, a method is known from the periodical“Brauwelt [Brewing World],” No. 17, 1988, pp. 666 ff, in whichregenerated diatomaceous earth is used as filter aid. The diatomaceousearth is regenerated with 4 to 5% sodium hydroxide at a temperature of80° C. To use the regenerated diatomaceous earth for another filtration,it is mixed with 10 to 20% diatomaceous earth that has not been used.With repeated use of regenerated diatomaceous earth by this method, anuncontrollable increase of the change of the pressure differential perunit of time is seen.

The invention is based on the task of creating a method for filteringliquids of the generic kind, which enables the use of regenerated filteraids.

This task is solved by a method with the characteristics of claim 1.

Regenerated filter aid is usable on an industrial scale only if theprocess is controllable. It is important for this for the increase ofthe pressure differential, which is the difference of the pressuresbefore and after the filter, to be controllable. As the inventor hasestablished, the increase of the pressure differential per unit of timeis highly dependent on the pressure differential at the start offiltration. If a filter aid that consists chiefly of filter aid that hasnot been regenerated is used in the precoating phase, the difference ofpressure at the start of filtration will be low and the increase of thepressure differential will be controllable. Mainly regenerated filteraid can be used for the filtration phase, since it has only a smalleffect on the increase of the differential pressure. The use of 0%regenerated filter aid for the precoat phase and 100% regenerated filteraid for the filtration phase is seen as the optimum design of theprocess. The regenerated filter aid is treated with an agent in theentire pH spectrum.

Diatomaceous earth is expediently used as filter aid. However, celluloseand/or perlites with or without diatomaceous can also be used as filteraids. It is foreseen that the method includes a regeneration phase, inwhich the filter aid is regenerated, and the regeneration is carried outin particular in the filter. Expediently, the regeneration phaseincludes the treatment of the filter aid with an alkali solution.Preferably, sodium hydroxide in a concentration from 0.1 to 2%, inparticular 0.5%, is foreseen as alkali solution. The substances that areto be removed from the filter aid are not dissolved in the sodiumhydroxide solution at concentrations under 0.1%. At alkali solutionconcentrations over 2% the structure of the diatomaceous earth isattacked, due to which the diatomaceous earth forms smaller intersticesfor the liquid in the precoat layer and thereby the pressuredifferential of the precoat rises considerably.

Expediently, the regeneration is carried out with alkali solution at atemperature from 60° C. to 90° C. It is further foreseen that the filtercake is rinsed with hot water, which in particular has a temperaturefrom 40° C. to 90° C., before the alkali solution treatment. Preferably,after the treatment with alkali solution, the alkali solution isdisplaced with hot water and with cold water. To neutralize the alkalisolution it is foreseen that the filter aid is treated with an acid, inparticular with nitric acid, and this process step is expedientlycarried out after the alkali solution has been displaced with hot andcold water. For a subsequent step it is foreseen that the acid isdisplaced with cold water and the liquid is then allowed to be drainedfrom the filter. Expediently, the filter aid is resuspended at the endof the regeneration phase.

An embodiment example of the invention is illustrated in more detail bymeans of the drawing. Here:

FIG. 1 shows a plant drawing of a block plant for conducting the method,

FIG. 2 shows a graphical representation of the dependence of thepressure differential at the end of filtration on the pressuredifferential at the start of filtration.

FIG. 1 shows a plant diagram of a block plant for precoat filtration, inwhich is schematically represented a filter 1, which is designed as acentrifugal horizontal filter. Filter 1 consists of a housing 17 withfilter elements arranged in it consisting of disk shaped filter cells 2stacked one on the other and a central channel 3. The central channel 3lies downstream from the filter element packet and therefore forms thefiltrate side, while the space between the filter cells 2 and thehousing 17 of filter 1 forms the feed side. To deliver the feed, thefilter 1 has a hollow shaft 18, which is arranged coaxially to centralchannel 3 and surrounds this channel, forming an intermediate space fordelivery of the feed. The hollow shaft 18 has orifices 19, through whichthe feed can flow to the feed side of the filter cells 2. Instead of thefilter elements, the filter 1 can also contain a cartridge filter asfilter surface. Filter 1 has an air escape 6. From the feed side a drainpipe 7 leads to a tank 4, which contains regenerated diatomaceous earthas filter aid. Another tank 5 contains “neugur,” i.e., diatomaceousearth that has not been regenerated. Cellulose and/or perlite can alsobe added to the diatomaceous earth as filter aid. It is also possible touse a filter aid that consists only of cellulose and/or perlite. Theaddition of silica gel is also possible, but silica gel cannot beregenerated and must therefore be readded to the regenerated filter aid.

Before the beginning of filtration the filter 1 is coated from tank 5via a refill pipe 15 with filter aid that has not been regenerated, forexample diatomaceous earth, where the diatomaceous earth is deposited inparticular with water. The precoating is dependent on the filtermaterial and can amount to for instance 600 g filter aid for m² filterarea. The diatomaceous earth is, for the coating, transferred via pump 9and feed conduit 14 to the feed side of filter cells 2 of filter 1.During the precoating the diatomaceous earth can be mixed with up to 30%regenerated diatomaceous earth from tank 4.

After precoating, the feed is conveyed to the feed side of filter 1 viathe feed line 8 by means of pump 11 through the feed line 14 into thehollow shaft 18 and through the orifices 19. Regenerated diatomaceousearth from tank 4 is added to the feed via pump 9, and a portion of notregenerated diatomaceous earth from tank 5 can also be added. Thefiltrate, after filtration, leaves filter 1 via filter outlet 12. Thefiltration is interrupted if the pressure differential at filter 1reaches a preset value or if the filter cake that is formed through theadded filter aid reaches a preset size.

After stopping filtration the filter aid or the diatomaceous earth infilter 1 is regenerated. For this filtrate that is still in filter 1,especially if after interrupting filtration the quality of the filtratecould no longer be ensured, is sent back to the feed. The feed isdiverted. Then the filter 1 is filled with hot water, which can have atemperature of about 40° C., and the filter cake is flushed at atemperature rising to about 90° C. After the rinsing operation, sodiumhydroxide is added so that an approximately 0.5% sodium hydroxidesolution results. However, potassium hydroxide solution can also beused. The alkali solution temperature is about 60 to 90° C. The sodiumhydroxide solution is circulated through the diatomaceous earth. Thetreatment of the diatomaceous earth with sodium hydroxide solution cantake about 30 minutes, for example. Then the alkali solution isdisplaced with hot water and cold water. As this happens it is cooled toabout 20° C. In the next step of the method nitric acid is added and thediatomaceous earth is rinsed with it, for example for 5 minutes. Thenitric acid is then displaced with cold water and then the remainingliquid is drained from filter 1.

To resuspend the filter cake, the filter element packet is set intorotation and the filter cake is spun off. The regenerated filter aidslurry that is trapped in the lower part of filter 1 is forced back totank 4 via drain pipe 7 by means of gas. During the cleaning of thefilter the filter elements 2 can be sprayed off by means of a spraystrip 20 arranged in the filter housing 17. The spray strip 20 issupplied from a feed pipe 10.

FIG. 2 shows the relationship between the pressure differential at theend of filtration a and the change of the pressure differential per unittime b against the pressure differential at the start of filtration. Thepressure differential at the start of filtration a is plotted on theaxis 21, while the change of the pressure differential at the end offiltration b is plotted on axis 22, and the pressure differential at thestart of filtration is plotted on axis 23. It is clear from the diagramthat the pressure differential at the end of filtration a and thepressure differential per unit of time b are considerably dependent onthe pressure differential at the start of filtration. The smaller thepressure differential is at the start of filtration, the lower will bethe pressure differential at the end of filtration a and the change ofthe pressure differential per unit of time b. Precoating with filter aidthat has not been regenerated produces a low pressure differential atthe start of filtration and thereby a low pressure differential at theend of filtration a as well as a low increase of pressure differentialper unit of time b.

The method for filtering liquids can be used in particular forbiological liquids. It is important for the regeneration of the filteraid with alkali solution that the substances that are filtered out besoluble in alkali solution.

The method can be used in today's precoat filters. Tank filters likehorizontal filters or cartridge filters are favorable for the use of themethod, but the method can basically also be used in frame filters aswell. The method can also be used in combination with the method forstabilizing tannin- or protein-containing liquids, for example withPVPP, or with a method in which a prepared filter cake is used.

1. A method for filtering liquids, in which a filter is precoated withfilter aid in a precoating phase and feed is filtered while addingfilter aid in a subsequent filtration phase, where the filter aid formsa filter cake on the filter in the precoating phase and the filtrationphase, wherein in the precoating phase, filter aid is deposited in whichthe amount of regenerated filter aid is <30%, and filter aid is added inthe filtration phase that chiefly consists of regenerated filter aid,where the regenerated filter aid has been treated with an agent in therange of the overall pH spectrum.
 2. A method as in claim 1, wherein inthe filtration phase filter aid is added that consists nearly entirelyof regenerated filter aid.
 3. A method as in claim 1, whereindiatomaceous earth is used as filter aid.
 4. A method as in claim 1,wherein cellulose and/or perlite with or without diatomaceous earth isused as filter aid.
 5. A method as in claim 1, wherein silica gel and/orPVPP is added to the filter aid.
 6. A method as in claim 1, wherein themethod includes a regeneration phase, in which the filter aid isregenerated.
 7. A method as in claim 6, wherein the regeneration iscarried out in the filter.
 8. A method as in claim 6, wherein theregeneration phase includes the treatment of the filter aid with analkali solution.
 9. A method as in claim 8, wherein the alkali solutionis sodium hydroxide solution in a concentration of 0.1 to 2%.
 10. Amethod as in claim 8, wherein the regeneration with alkali solution iscarried out at a temperature from 60° C. to 90° C.
 11. A method as inclaim 8, wherein the filter cake is rinsed with hot water before thetreatment with alkali solution.
 12. A method as in claim 11, wherein thehot water has a temperature from 40° C. to 90° C.
 13. A method as inclaim 8, wherein after treatment with alkali solution the alkalisolution is displaced with hot water and with cold water.
 14. A methodas in claim 6, wherein the filter aid is treated with an acid.
 15. Amethod as in claim 14, wherein the filter aid is treated with nitricaid.
 16. A method as in claim 14, wherein the treatment with acid iscarried out after displacing the alkali solution with hot water and withcold water.
 17. A method as in claim 14, wherein the acid is displacedwith cold water and the acid is then allowed to drain from the filter.18. A method as in claim 6, wherein the filter aid is resuspended at theend of the regeneration phase.
 19. A method as in claim 1, wherein themethod is carried out in combination with a method for stabilizingtannin-containing liquids.